Toledo - Switzerland's Fabien Cancellara pulled out of the Tour of Spain before the end of the 19th stage Friday, raising concerns over his participation in the world road race championships.
Cancellara is the reigning world and Olympic time trial champion and had been set to compete in both the road and time trial in Geelong, Australia during the week of September 29-October 3.
However after a successful but tough racing season the Saxo Bank rider came into the three-week race complaining of fatigue and his abandon on Friday raises fresh concerns over his form.
Two days after being beaten into third place in a pancake flat time trial over 46 km, the normally unshakable Cancellara pulled out after 120km of racing in the 231 km stage between Piedrahita and Toledo, according to organisers.
He recently said any decision on his participation in the worlds would depend on whether he was "at 100 percent of my abilities".
Cancellara has won the world time trial crown three times and, on form, he would line up as favourite for an all-time record fourth gold medal in the race against the clock.